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From "Suresh Srinivas (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8217) Edge case split-brain race in ZK-based auto-failover
Date Wed, 28 Mar 2012 04:57:29 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8217?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13240171#comment-13240171
] 

Suresh Srinivas commented on HADOOP-8217:
-----------------------------------------

Todd, I think this has been brought up in other comments as well. I am very uncomfortable
with just creating jiras for each scenarios as we think of, instead of capturing it in a design
document. I cannot keep up with jiras, that are created and committed in short periods of
time. I do not want to comment on jiras asking for time and impede progress. A design document
helps here. Perhaps, we should setup a meeting to go over the design, and discuss issues in
more detail.
                
> Edge case split-brain race in ZK-based auto-failover
> ----------------------------------------------------
>
>                 Key: HADOOP-8217
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8217
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: ha
>    Affects Versions: 0.24.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>
> As discussed in HADOOP-8206, the current design for automatic failover has the following
race:
> - ZKFC1 gets active lock
> - ZKFC1 is about to send transitionToActive() and machine freezes (eg GC pause + swapping)
> - ZKFC1 loses its ZK lock, ZKFC2 gets ZK lock
> - ZKFC2 calls transitionToStandby on NN1, and transitions NN2 to active
> - ZKFC1 wakes up from pause, calls transitionToActive(), now we have a bad situation
> This is rare, since it requires ZKFC1 to freeze longer than its ZK session timeout, but
worth fixing, since the results can be disastrous.

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